1. Field of the Invention
Aspects of the present invention generally relate to a turbo stream processing device and method for robustly processing a transmission stream for digital broadcasting. More particularly, aspects of the present invention relate to a turbo stream processing device and method for more robustly processing a turbo stream of a dual transmission stream which includes a normal stream and the turbo stream and transmitting the dual transmission stream to improve a reception performance of an Advanced Television Systems Committed (ATSC) Vestigial Sideband—(VSB) system such as is used in the U.S.A. terrestrial Digital Television (DTV) system.
2. Description of the Related Art
A single-carrier ATSC VSB system, such as is used in the U.S.A. terrestrial digital broadcasting system, uses a single field sync per 312 segments. Hence, its reception performance is not good in a poor channel environment, especially, in a Doppler fading channel.
FIG. 1 is a block diagram of a transmitter and a receiver, as used in a general U.S.A. terrestrial digital broadcasting system, in conformity with the ATSC DTV standard. The digital broadcasting transmitter of FIG. 1 uses the Enhanced Vestigial Sideband (EVSB) system suggested by Philips, and is constructed to generate and transmit a dual stream by adding robust data to a normal stream of the conventional ATSC VSB system.
As shown in FIG. 1, the digital broadcasting transmitter executes an error correction coding by including a randomizer 11 for randomizing the dual stream, a Reed-Solomon (RS) encoder 12 which is a concatenated encoder for adding a parity byte to the transmission stream to correct errors occurring due to the channel characteristics during the transmission, an interleaver 13 for interleaving the RS-encoded data in a certain pattern, and a trellis encoder 14 to map data to eight-level symbols by trellis-encoding the interleaved data at ⅔ rate.
The digital broadcasting transmitter further includes a multiplexer 15 for inserting field sync and segment sync into the data which passed through the error correction coding, as shown in FIG. 2. The digital broadcasting transmitter also includes a modulator 16 to insert a pilot tone by adding a certain DC value to the data symbols having the inserted segment sync and field sync; 2) perform a VSB modulation through a pulse shaping; 3) up-convert to an RF channel band signal, and 4) transmit the converted signal.
Accordingly, the digital broadcasting transmitter multiplexes (not shown) and applies the normal data and the robust data to the randomizer 11 according to the dual stream scheme which transmits the normal data and the robust data in one channel. The input data is randomized at the randomizer 11, the randomized data is outer-encoded (block encoded) at the RS encoder 12 which is an outer encoder, and the outer-encoded data is interleaved at the interleaver 13. The interleaved data is inner-encoded (convolution encoded) by twelve symbols at the trellis encoder 14 and mapped to eight-level symbols. The field sync and the segment sync are then inserted to the mapped data. Next, the pilot tone is inserted, VSB modulation is performed, and the result is converted to a radio (RF) signal. Finally, the RF signal is transmitted.
The digital broadcasting receiver of FIG. 1, includes a tuner (not shown) to convert the RF signal received through the channel into a baseband signal; a demodulator 21 to perform the sync detection and the demodulation of the converted baseband signal, an equalizer 22 to compensate for multipath-based channel distortion in the demodulated signal; a viterbi decoder 23 to correct errors in the equalized signal and to decode the equalized signal into symbol data; a deinterleaver 24 to deinterleave the decoded symbol data; an RS decoder 25 to correct errors; and a derandomizer 26 to derandomize the error-corrected data and output the resulting MPEG-2 transmission stream.
Hence, the digital broadcasting receiver of FIG. 1 recovers the original signal in the inverse operation of the digital broadcasting transmitter by down-converting the RF signal to the baseband signal, demodulating and equalizing the converted signal, and decoding the demodulated and equalized signal.
FIG. 2 shows an example VSB data frame (with inserted segment sync and field sync signals) such as is used in the U.S.A. digital broadcasting (8-VSB) system. As shown in FIG. 2, one frame consists of 2 fields. One field consists of a field sync segment, which is the first segment, and 312 data segments. In the VSB data frame, each segment corresponds to one MPEG-2 packet, and consists of a 4-symbol segment sync and 828 data symbols.
In FIG. 2, the segment sync signal and the field sync signal are used by the digital broadcasting receiver for synchronization and equalization. In other words, the contents of the field sync and the segment sync are previously known to both the digital broadcasting transmitter and the digital broadcasting receiver and used as reference signals to synchronize and equalize the transmission received by the digital broadcasting receiver.
The U.S.A. terrestrial digital broadcasting system of FIG. 1 is constructed to generate and transmit a dual stream by adding the robust data to the normal data of the conventional ATSC VSB system in order to transmit the robust data and normal data together.
However, disadvantageously, the U.S.A. terrestrial digital broadcasting system of FIG. 1 cannot enhance the poor reception performance of the normal data stream in the multipath channel even when the transmitted dual stream includes the added robust data. That is, the reception performance is not improved at all even with the augmented normal stream. In addition, with respect to the turbo stream, the reception performance does not show great improvement in the multipath environment. Hereinafter, the normal data stream and turbo data stream are referred to as normal stream and turbo stream, respectively.
Therefore, a demand arises for a technique to more robustly process the turbo stream in order to enhance the reception performance in relation to the turbo stream.